A new article about congenital amusia has just been published in Cerebral Cortex by Krista Hyde, Robert Zatorre and Isabelle Peretz. As you can expect I was extremely interested in their findings! (see previous posts for details of my work in congenital amusia). Neuroscience studies of amusia are quite rare largely because of the difficulty in generating large enough groups of participants. However, when they do happen these studies are fascinating as they provide a unique insight into how the brain processes music.
What did we know so far about the brain in amusia? Krista’s previous studies and those from other labs too (e.g. Mandell et al, 2007, Loui et al, 2009), have indicated that amusia is associated with abnormalities in the way that the gray and white matter of the brain is organised in the auditory and frontal cortices. One theory is that amusia is a ‘disconnection syndrome’ – meaning that the white matter pathways that carry information about music (mostly pitch) from the auditory areas of the brain to the frontal areas have not fully developed in individuals with congenital amusia.
So far however, we have been relying almost exclusively on anatomical studies of amusia to form conclusions, using techniques that tell us about the size, density and location of different brain structures (e.g. MRI and VBM). This new study uses instead a functional technique (fMRI) which reveals how the brain is actually responding to sound, by identifying changes in cerebral blood flow and oxygen consumption.
Participants in the study listened to short melodies where the pitches changed or stayed the same. Results indicated that the auditory cortex of amusics could track small changes in pitch. However, one area in the frontal cortex of amusics, the inferior frontal gyrus (IFG), showed decreased activity in response to changing pitches, whereas in controls the same conditions resulted in increased activity. The IFG is thought to be important for the conscious, attentive monitoring of pitch changes in a melody.
The authors then go on to talk about a second finding: Increased connectivity between the two brain hemispheres in amusics compared to controls. They suggest that this might have happened in amusics because the brain is compensating for the poor response in the forward auditory pathways. If this is true it might be a parallel finding to that of increased hemisphere connectivity in dyslexia (Wolf et al, 2010).
Overall this paper adds further evidence to support the hypothesis that there is a degree of disconnection between auditory and frontal areas of the brain in individuals with congenital amusia. In other words, amusics may have the ability to process musical sounds in their brain; the problem might be that they don’t have conscious access to this knowledge.
Paper: Hyde, K., Zatorre, R. & Peretz, I. (2010) Functional MRI Evidence of an Abnormal Neural Network for Pitch Processing in Congenital Amusia. Cerebral Cortex. (http://www.brams.umontreal.ca/plab/publications/from_author/peretz_i)
Loui P, Alsop D, Schlaug G. 2009. Tone deafness: a new disconnection syndrome? J Neurosci. 29:10215–10220.
Mandell J, Schulze K, Schlaug G. 2007. Congenital amusia: an auditorymotor feedback disorder? Restor Neurol Neurosci. 25:323–334.
Wolf RC, Sambataro F, Lohr C, Steinbrink C, Martin C, Vasic N. 2010.Functional brain network abnormalities during verbal working memory performance in adolescents and young adults with dyslexia. Neuropsychologia. 48:309–318